Steam seal diverting valve



Jan. l, 1963 P. G. IPSEN STEAM SEAL DIVERTING VALVE Filed NOV. 6, 1961.IOP-3m I OmPZOO .2326.2

.. Imll@ INVENTOR: PETERAG. PSEN, 4J, @A1545 HIS ATTORNEY.

United States atellt emesse STEAM SEAL DFJERTHNG VALVE Peter G. Ipsen,Schenectady, NY., assigner to General Electric Company, a corporation ofNew York Filed Nov. 6, 1961, Ser. No. 150,319 Claims. (Cl. dil- 64) Thisinvention relates to steam turbine power plants of the type wherehigh-temperature gland seal packing steam may have access, under someoperating conditions, to turbine sections designed for lowertemperatures, and is a system for protecting these turbine sectionsagainst unwanted entry of the gland seal steam.

The sealing of the shaft against steam leakage in a steam turbine powerplant is generally accomplished by means of labyrinth-type shaftpackings, which provide a series of throttlings limiting steam leakagealong the rotating shaft. Some of the packings are vacuum packings whichnormally require an iniiow of steam While other packings are pressurepackings which have an outllow of steam. In order that the pressurepackings can furnish steam to the vacuum packings, so that a vbalance inmass flow of steam in and out of diliferent packings will occur ataround half load, a common gland steam header is used to service bothvacuum packings and pressure packings. At low loads, however, thepressure packings furnish insullicient steam to balance the flow andadditional steam must be added. This additional steam is usuallysupplied from the primary steam line. Conversely, at high loads, thegland header is supplied with too much steam, and the excess must bedischarged. A steam seal regulator performs the function of adding steamor discharginU excess steam as required, so as to maintain a regulatedpressure in the header. Excess packing steam from the header has, insome cases, been diverted to the condenser of the steam turbine.

Turbine power plants of this type often utilize lowpressure steamextracted from a relatively low-temperature, low-pressure turbine in aheat exchanger' to heat the feed water. In order to improve the etciencyof the power plant, the excess gland steam has often been added to theextraction steam, thereby adding additional energy to the feed water.This invention is directed to certain problems arising in thisparticular arrangement under abnormal operating conditions.

if the turbine is operating at light load, and if more packing steam issupplied to the gland header than is required, the hot steam may flowbackwardly through the extraction line into the turbine instead of tothe feedwater heater. Since the low-pressure turbine is not designed forsteam of this temperature, there is a possibility of overheating thelow-pressure turbine parts.

A similar condition can occur if the feedwater heater stops operating.Excess gland seal steam which has access to the extraction line mayagain flow to the turbine with possible overheating.

Although the conditions mentioned above could be corrected by means of asimple temperature measuring device in the extraction line, such adevice would very rarely be called upon to operate. Therefore, it isdesirable that protective components be provided which are exercisedautomatically during normal startup and shutdown, so as to insure theircomplete reliability. Accordingly, one object of the present inventionis to provide an arrangement for protecting the low-pressure turbineparts from unwanted entry of gland seal steam.

Another object of the invention is to providey an arrangement forobtaining the increased etliciency resulting when excess gland sealsteam is mixed with the extraction steam to heat the feedwater, whileproviding means to protect the turbine under abnormal operatingconditions.

Another object of the invention is to provide components protecting thelow-pressure turbine against unwanted entry of high-temperature steam,where the components are periodically exercised.

A more specific object of the invention is to provide an arrangementwhich mixes excess gland seal steam with the extraction steam but whichdiverts excess gland seal steam to the condenser under certainconditions which might cause unwanted entry of the gland seal steam orprimary steam into the low-pressure turbine.

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespeciiication. The invention, however, both as to organization andmethod of practice, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription, taken in connection with the accompanying drawings in whichthe single FIGURE Aof the drawing is a simplified schematic View of thesystem.

Referring to the drawing, a low-pressure turbine section l is showndischarging steam through an exhaust hood 2 to a condenser 3. Turbine 1extracts the last bit of energy from steam which has been previouslyexpanded in other turbine sections (not shown). Since turbine 1 operatesat relatively low -steam pressures, usually below atmospheric pressureand in a saturated condition, the rotating parts are not designed forhigh temperatures. A small amount of feedwater heating steam isextracted from turbine 1 through an extraction line 4, .and is employedto supply heat to the condensate in `feedwater heater 5 in a well-knownmanner. The extraction pressure in extraction line l may be of the orderof l0 pounds per square inch absolute.

The shaft packings of the various turbine sections (not shown) aresupplied with gland scaling steam. The gland steam is often maintainedat a regulated pressure, for example on the order of 4 pounds per squareinch gage, in a gland header, such as indicated at 6. Gland header 6supplies gland seal steam to or accepts steam from the ipackings (notshown) through conduits 6a. The steam for gland header 6 is furnishedfrom a source of highpressure, high-temperature primary steam (notshown) through a pipe 7, and pipe 8, to a steam seal regulator indicatedgenerally as 9. A manual valve 10 may be employed to cut oil the ow ofsteam to regulator 9.

Gland header conduits 6a are connected to packing chambers or" differentpressure levels in such a way that at a given constant load, there is noneed for adding steam to header 6. However, variable loadings on theturbine dictate the need for a gland seal steam regulator 9. The`details of the regulator 9 are not material to the present invention. Asuitable regulator for this purpose is disclosed in US. Patent2,681,044, issued to M. A. Eggenberger on lune l5, 1954, and assigned tothe assignee of the present application. Regulator 9 maintains aconstant pressure in gland header 6 by means of a steam seal feed valve12. Regulator 9 also includes an unloading valve 13 which dischargesexcess steam to a discharge pipe '1li when there is excess steam inheader 6. Normally, steam seal feed valve 12 will be closed kwhenunloading valve 13 is open, and vice versa, but there is always apossibility in unusual cases that steam seal feed valve 12 might stickin an open position at the same time that unloading valve 13 is open. Inthis case, primary steam would flow from the high-pressure inlet pipe Sto the regulator discharge pipe i4.

A manually-operated regulator bypass valve 15 is provided to supplyprimary steam from pipe 7 directly to gland header 5 through a pipe 16.Bypass valve 15 may Patented Jan. l, 1963A be used under emergencyconditions to supply gland -seal steam if regulator 9 becomesinoperative. However, when the operator opens manual bypass valve 15,and if unloading valve 13 in the regulator 9 is open, hot steam can alsoflow through pipes 16, 11, through the regulator 9, to discharge pipe14.

Under normal operating conditions, however, for example above 50% load,it is greatly desirable for excess gland seal steam to llow through pipe14 to extraction line 4, 'where it mixes with the extraction steam so asto supply additional energy to heat the eedwater in feedwater heater 5.

According to the present invention, a three-way valve 17 is interposedin pipe 14 between regulator 9 and extraction line 4. Three-way valve 17may be of any suitable type suiicient to pass the designed steam llow,but as shown here comprises two butterfly valves 17a, 1711 operated by asingle actuator rod 18. The butterfly valves are arranged in a mannerwhich will be obvious from the drawing, so that valve 17a is open whenvalve 17b is closed, and vice versa. The normal operating position ofthree-Way valve 17 is as shown, with butterlly valve 17a open to admitexcess gland steam from line 14 to mix with extraction steam in line 4.

The alternate outlet of valve 17 controlled by butterliy valve 17h isconnected to condenser 3 by means of a pipe 19. Thus, when the actuatorrod 18 is moved to the other position, steam will flow from line 14through pipe 19 to condenser 3, rather than to extraction line 4.

Three-way valve 17 is operated by a servo motor which may be of any-suitable type, but as shown comprises an air cylinder 20 having aspring-loaded piston 21 connected to actuator 18 by piston rod 22. Whenair is supplied to the lower end of cylinder 2li, the air pressure holdsthree-way valve 17 in the position shown. When air pressure is releasedin cylinder 20, the spring will move three-way valve 17 so as to divertsteam from pipe 14 to condenser 3.

The air which holds the piston 21 against its spring in cylinder 2t? isfurnished from a source of high-pressure air (not shown) at a pressurewhich may be on the order of 80 p.s.i. The air ilow is indicated astaking place through pipes indicated by dot-dash lines, and flows in thedirection shown by the arrows through three pilot valves in successionindicated at 23, 24, 25 respectively.

l All three pilot valves 23-25 are arranged to provide freecommunication for the air from the high-pressure source to cylinder 20under normal operating conditions. Any one ofthe series-connected pilotvalves, however, may discharge air from cylinder 2t) and divert steam tothe condenser when any one of three selected abnormal operatingconditions occur.

Referring first to pilot valve 23, it will be seen that the valve isarranged to discharge air from cylinder 20 unless the stem 23a is helddown against the action of a spring 2317. However, if pilot valve stem23a is held down in the position shown, air can ilow freely to cylinderZ6 unless the remaining pilot valves 24, 25 block the flow. Valve stem23a is held down by a projection 26 which is raised and lowered when thehandle 27 of bypass valve 15 is Vmanually operated. Thus, wheneverbypass valve 15 is open, so that primary steam from line 7 might ow intopipe 14, pilot valve 23 unloads, thus operating three-way valve 17 todivert the steam to condenser 3..

The second pilot valve 24 is cam-operated by a lever 28 actuated by thestem of steam seal feed valve 12. Whenever the steam seal feed valve 12is open, lever 28 moves pilot valve stem 24a to compress the spring 2419so as again toV operate the three-way valve to divert steam tothecondenser.

The third pilot valve 25 has a spring-loaded stem 25a actuated by asolenoid 29. When the solenoid is energizd"throgh'electrical leadsVindicated by dashed line Cil (lil

36, stem 25a is held against the spring to permit threeway valve 17 toremain in the left-hand position as shown. When the power in leads Silis removed, the air is dumped from the cylinder 20 and three-way valve17 again diverts steam to the condenser. The power in leads 30 tosolenoid 29 is controlled by a temperature-responsive device measuringthe steam temperature in extraction line 4. This is indicated by athermostat 31 which operates a relay 32 supplied with a suitable sourceof electrical energy (not shown) through leads 33. Relay 32 is connectedto energize solenoid 29 through leads 30, 33 when thermostat 31indicates that the steam in extraction line 4l is at a safe operatingtemperature. Relay 32 may also be provided with a manual control knob 34which can be used to test the operation of three-way valve 17.

The operation and advantages of the protective system are as follows.The drawing indicates the valve positions when the turbine is under fullload conditions. No primary steam is entering header 6. Under theseoperating conditions, the steam pressure in gland header 6 is regulatedby regulator 9 and excess steam is being supplied to pipe 1d, flowingthrough three-way valve 17 to mix with the extraction steam inextraction line 4. This addition of heat energy to the extraction steamimproves the etliciency. Three-way valve 17, however, is arranged todivert steam from pipe 14 to the condenser, thereby protecting theblading and other members in low-pressure turbine 1, whenever certainoperating conditions, as explained below, would raise the temperature inextraction line 4- to abnormal levels.

Assuming that regulator 9 is operating properly, feedwater heater 5 maynevertheless cease to operate, in which case the excess gland seal steamfrom gland header '6 will cause the temperature in extraction line 4 torise to unsafe levels. This will actuate thermostat 31 insolenoid-actuated valve 25 to divert the gland seal steam to thecondenser.

Another condition which might damage the elements in turbine 1 occurs ifsteam seal feed valve 12 sticks open under light load conditions. Inthis case, when load is increased to the point where primary steam is nolonger required, the high-temperature primary steam from pipe 7 wouldflow directly through the open unloading valve 13, through pipe 1d,through-extraction line 4, and into turbine 1. However, as explainedpreviously, whenever steam seal feed valve 12 is open, the cam-operatedpilot valve 24 is tripped and the three-way valve 17 is connected todivert the gland steam from pipe 14 to the condenser.

Another potentially unsafe condition can take place where the operatordesires to manually admit steam through bypass valve 15. As explainedabove, when bypass valve 15 is opened, pilot valve 23 will discharge airfrom cylinder 2@ which holds three-way valve 17 in the position shown,and again diverts the hot steam to the condenser.

Although three pilot valves have been shown which are actuated by threedifferent selected operating conditions, tending to raise thetemperature in the extraction conduit 4, it should be apparent thatgreater or fewer selectedV conditions could be used to operate thethreeway valve. For example, high water level in feedwater heater 5would indicate that the steam ow to the heater should be reduced so asnot to overheat the low-pressure turbine. Therefore, a float-operatedswitch or pilot valve couldbe employed to actuate the three-way valve17. Therefore, the system derives the benefits oi mixing lie excessgland seal steam with the extraction steam for increased eiiiciency, butat the same time protects the; low-pressure turbine under unusualoperating conditions: by means of a three-way valve which passes thesteam harmlessly to the condenser.

lt will be observed that while only the single condi-- tion oftemperature in the extraction conduit as measured by thermostat 31 mightbe sulicient in some cases, the three-way valve 17 and its associateservo motor would rarely be called upon to operate. Therefore, in orderto insure reliability, it is preferred that components be employed whichare exercised during normal startup and shutdown. It will be seen thatthe pilot devices 23 and 25 are actuated by the bypass valve 15 and bythe regulator valve 12 respectively, which would normally be operativeat low loads. These pilot devices exercise the three-way valve at theselow loads where the coitnecting of the three-way valve to the condenseris of little consequence. However, the three-way valve Yis reconnectedto the extraction line for good efficiency at high loa-ds, and thus isexercised automatically.

While what has been described is felt to be the preferred embodiment ofthe invention, other modifications will occur to those skilled in theart, and it is of course desired to cover in the appended claims allsuch modifications as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a steam turbine having steam sealed shaft packings requiringrelatively high-temperature sealing steam, and including a low-pressureturbine section subject to overheating by excess sealing steam andexhausting to a condenser, the combination of:

a steam extraction conduit connected to the low-pressure turbinesection,

a gland seal steam header containing high-temperature gland seal steam,regulating means maintaining a preselected pressure .in said glandheader and including rst valve means discharging excess gland seal steamfrom the regulating means through a discharge outlet,

three-Way valve means including conduits connecting the regulating meansdischarge outlet with the extraction conduit when the three-way valve isin a first position and connecting the regulating means discharge outletwith the condenser when the threeway valve is in a second position,

servo motor means connected to operate said threeway valve means,

and a plurality of pilot means operatively connected to the servo motormeans, each of said pilot means being actuated to cause the servo motormeans to move the three-way valve means to said second position when aselected condition indicates that excessi-ve high-temperature glandsteam may be ilowing through said regulating means and through theextraction conduit to the low-pressure turbine section, whereby any ofsaid conditions will cause the three-way valve means to diverthigh-temperature gland seal steam from the extraction conduit to thecondenser.

2. The combination according to claim l, including a bypass valveadmitting high-temperature steam around said regulating means to saidgland header, and having 6 means actuating one of said pilot means whensaid bypass valve is open.

l3. The combination according to claim l, wherein said regulating meansIincludes second valve means admitting high-temperature steam to saidheader and means causing said second valve means to actuate one of saidpilot means when the second valve means is open.

4. The combination according to claim 1, including temperatureresponsive means disposed in said extraction conduit, and solenoid meansactuating one of said pilot means when a preselected temperature isexceeded in the extraction conduit.

5. In a steam turbinepower plant having gland seal shaft packingsrequiring relatively high-temperature sealing steam and including alow-pressure turbine section subject to possible overheating byexcessive high-temperature steam and exhausting to a condenser, thecombination of:

a steam extraction conduit connected to the low-pressure turbinesection,

a gland seal steam header furnishing sealing steam to the shaftpackings,

a source of primary high-temperature steam,

regulating means connected between said steam source and said glandheader, and including first admission valve means admitting steam tosaid gland header, and second discharge valve means discharging excessgland seal steam from said header,

a bypass valve connected between said steam source and said glandheader, bypassing said regulating means,

three-way valve means including first connecting conduit means supplyingexcess gland seal steam from said regulating means to said extractionconduit when the three-way valve means is in a rst position and alsoincluding second connecting conduit means supplying excess gland sealSteam from said regulating means discharge to the condenser when thethree-way valve means is in a second position,

fluid-actuated servo means connected to operate said three-way valvemeans and biased toward the threeway valve second position,

a source of actuating fluid under pressure,

rst, second and third pilot valves connected in series between saidactuating uid source and said servo means, each pilot valve beinganranged to divert the source of actuating fluid from the servo meanswhen released,

means connected between said bypass valve and said first pilot valve torelease the first pilot valve when the bypass valve is open,

means connected between the regulating means rst valve and the second-pilot valve to release the second pilot valve when the regulating meansfirst valve is open, and

temperature responsive means disposed in said extraction conduit,including means to release said third pilot valve when a preselectedtemperature is exceeded in the extraction conduit.

No references cited.

1. IN A STEAM TURBINE HAVING STEAM SEALED SHAFT PACKINGS REQUIRINGRELATIVELY HIGH-TEMPERATURE SEALING STEAM, AND INCLUDING A LOW-PRESSURETURBINE SECTION SUBJECT TO OVERHEATING BY EXCESS SEALING STEAM ANDEXHAUSTING TO A CONDENSER, THE COMBINATION OF: A STEAM EXTRACTIONCONDUIT CONNECTED TO THE LOW-PRESSURE TURBINE SECTION, A GLAND SEALSTEAM HEADER CONTAINING HIGH-TEMPERATURE GLAND SEAL STEAM, REGULATINGMEANS MAINTAINING A PRESELECTED PRESSURE IN SAID GLAND HEADER ANDINCLUDING FIRST VALVE MEANS DISCHARGING EXCESS GLAND SEAL STEAM FROM THEREGULATING MEANS THROUGH A DISCHARGE OUTLET, THREE-WAY VALVE MEANSINCLUDING CONDUITS CONNECTING THE REGULATING MEANS DISCHARGE OUTLET WITHTHE EXTRACTION CONDUIT WHEN THE THREE-WAY VALVE IS IN A FIRST POSITIONAND CONNECTING THE REGULATING MEANS DISCHARGE OUTLET WITH THE CONDENSERWHEN THE THREEWAY VALVE IS IN A SECOND POSITION, SERVO MOTOR MEANSCONNECTED TO OPERATE SAID THREEWAY VALVE MEANS, AND A PLURALITY OF PILOTMEANS OPERATIVELY CONNECTED TO THE SERVO MOTOR MEANS, EACH OF SAID PILOTMEANS BEING ACTUATED TO CAUSE THE SERVO MOTOR MEANS TO MOVE THETHREE-WAY VALVE MEANS TO SAID SECOND POSITION WHEN A SELECTED CONDITIONINDICATES THAT EXCESSIVE HIGH-TEMPERTURE GLAND STEAM MAY BE FLOWINGTHROUGH SAID REGULATING MEANS AND THROUGH THE EXTRACTION CONDUIT TO THELOW-PRESSURE TURBINE SECTION, WHEREBY ANY OF SAID CONDITIONS WILL CAUSETHE THREE-WAY VALVE MEANS TO DIVERT HIGH-TEMPERATURE GLAND SEAL STEAMFROM THE EXTRACTION CONDUIT TO THE CONDENSER.